Blenheim wells may serve Renwick

When the creek is muddy, the water supply is muddy

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Piping Blenheim water to Renwick could be a way to beat water shortages and quality issues, the Marlborough District Council says.

A report to the council's assets and services committee meeting tomorrow says Renwick's water supply does not meet the Government's drinking water standards and it is in short supply during summer or in dry spells.

The water is drawn from Gibsons Creek. When the creek is muddy, the water supply is muddy. The water is also corrosive and is eating at the pipes, causing leaks.

Aeration treatment to reduce the corrosiveness is not working, and chlorine treatment to kill bacteria only works when the water is clear.

The report says chlorine at levels that are safe to drink was not effective against giardia and cryptosporidium, which make people sick when they reach certain levels.

Water could be drawn from wells on Conders Bend Rd, which had better quality but the same treatment requirements. The Conders Bend Rd wells would be also more reliable in summer.

The report says that to use the Conders Bend Rd wells as the source of water for Renwick would cost approximately $1.35 million for the pumps and pipeline.

This assumes that property owners would allow the pipeline to be installed across their land.

Treatment systems to bring Renwick's water supply up to government health standards had been estimated at $9.2 million, or $11,700 per house connection.

However, the report says, a slow sand filter could provide a cheaper alternative treatment system.

Using a slow sand filter followed by ultraviolet disinfection would reduce the risk of bacterial contamination and provide a consistently safer quality of water at or close to the requirements of the drinking water standards.

However, it would require 3 hectares of land, including a planted buffer to protect the water supply.

Pumping Blenheim's water to Renwick would cost about $600,000 less than building a water treatment plant in Renwick, the report said.

It would cost about $8.6m to build the pipeline and pumping station, but operating costs would be significantly less than a water treatment plant in Renwick.

Water meters would be installed, to help water conservation, and a focus on fixing leaking water pipes would be needed, the report said.

"It is estimated that 58 per cent of the water pumped into the reticulation could be lost.

"At night in the early hours when water use is expected to be only 0.5 litres per second, the actual flow is 15 L/s."

The council could look at recycling water or rainwater collection, but these had not worked that well in other areas, the report said.

Council staff propose to step up leak detection and water pipe repairs in Renwick, within existing budgets, and to consult with the Renwick community about water meters to be installed in 2018-19.

More work was needed before a particular water treatment measure could be recommended.